Coaxial switches



g. 14, 1956 R. E. CHARLES 2,759,152

COAXIAL SWITCHES Filed Aug. 19, 1952 16 INVENToR.

BY @my F? Za/Af L, mmf 1"/ @2% A TroR/VEK United States Patent() COAHAL SWITCHES Randolph E. Charles, Wayland, Mass., assignor to General Communication Company, Boston, Mass., a corporation of Massachusetts Application August 19, 1952, Serial No. 305,242

Claims. (Cl. 333-7) This invention relates to high frequency switches and more particularly to a novel micro-wave siwtch of the sliding type for switching waveguides such as co-axial lines.

In the switching of micro-wave waveguide lines and the like, it is desirable that the switch have electrical characteristics identical to those of the waveguide lines into which they are inserted in order to avoid discontinuities in such lines with a resulting high standing wave ratio. It is further desirable that the unused waveguide lines be suitably terminated to avoid any danger of feedback between the lines, this being particularly important in the case of an antenna switching circuit connecting a receiver and a transmitter to a common antenna.

It is an object of the present invention to provide a sliding switch for waveguides such as co-axial lines which very closely maintains the impedance characteristics of the waveguide lines into which it is inserted.

It is a further object of the present invention properly to terminate the unused waveguide lines in said switch to prevent feedback of a signal through said switch into said unused line.

It is a feature of the invention that at least a portion of the boundary of the waveguide through the switch is maintained unbroken to provide a xed continuous conducting longitudinal portion of the boundary of the waveguide to permit current ow through the switch.

It is a further feature of the invention that it is mechanically extremely simple, and easily adaptable to well known methods of switch construction.

For the purpose of more fully explaining my invention, reference is made to the following drawings disclosing a preferred embodiment thereof in which;

Fig. 1 is a longitudinal cross sectional View of the slide switch of my invention, and

Fig. 2 is a lateral cross sectional view of the switch of Fig. 1 taken on the line 2 2 of Fig. 1.

It may be pointed out that waveguides, of which a co-axial line is one form having a central conductor, are well known and in use. However, I have found that the principles of a square waveguide can be used in the construction of a sliding waveguide switch with very substantial advantages over heretofore known waveguide switches.

According to the present invention, the switching elements are made electrically identical to a square waveguide construction having the impedance characteristics of the wave-guide lines with which the switch is to be used. With such an arrangement, the electro-magnetic field is conned within the four sides of the square waveguide. As long as the electromagnetic eld is so confined, it is permissible, without adversely affecting the impedance characteristic of the switch, to have certain types of mechanical discontinuities in the switch construction. Such discontinuities cannot, however extend around the entire periphery of the waveguide since it is essential that at least a portion of the waveguide have the metallic boundary extending continuously and unbroken throughout the switch. With such an arrangement there will be no discontinuity in the switch adversely to affect the current ow, and yet the metallic boundary surrounding the waveguide will preserve the electromagnetic field despite minor discontinuities. If both conditions are satised, the switch will have the characteristics identical to that of the waveguide lines to which it is attached, and it will not adversely affect the standing wave ratio of such waveguide lines.

A sliding switch structure constructed according to the above principles especially adapted for use with coaxial lines is illustrated in Figs. 1 and 2. Such switch has a metallic body portion 12 having in its upper surface a recess 14 of generally rectangular cross section. Extending along the bottom of said body 12 are three co-axial line connectors 16, 20 and 24, said connectors having central conductors 17, 21 and 25 mounted in suitable insulating blocks 18, 22 and 26. The outer portion of said connectors 16, 20 and 24, is suitably mounted as by screw threads on switch body 12, and said connectors 16, 20 and 24 extend through the switch body 12 to recess 14, the central conductor of each of said connectors extending through the switch body 12 substantially flush with the bottom surface of recess 14.

The sliding switch member 30 is preferably of metallic construction and arranged to fit closely within the side walls of recess 14, said switch member being slightly shorter than the chamber 14 for limited sliding linear movement within said chamber, as hereinafter more fully explained. The switch body has in its lower surface two identical metallic walled waveguide cavities 32, each of said cavities being of suitable cross sectional dimensions to form, together with the metallic-walled bottom of recess 14, a square coaxial line having impedance characteristics identical to that of the co-axial lines attached to connectors 16, 20 and 24. Waveguide cavities 32 are preferably both positioned along the longitudinal axis of switch member 30 along the bottom surface thereof and are separated from each other by a web 34 forming an integral portion of said member 30. Each of said cavities 32 has mounted centrally thereof a block of insulating material 33 having a central bore 36 therein. Central switch conductors 38 are mounted in said bores 36, said central switch conductors being of inverted U-shaped configuration and of a length sufficient to connect the central conductor 21 of inner co-axial line connector 20 with one of the conductors 17 or 25 of outer connectors 16 or 24. The conductors 38 are mounted loosely in bores 36 to allow limited sideway movement transversely of said bores, spring means being provided to urge said conductors 38 downwardly into rm pressure contact with co-axial line conductors 17, 21 and 2S. The spring means includes a spring 40 mounted in a recess 41 within sliding switch member 30, said spring 40 pressing downwardly against a pin 42 mounted in fixed position on conductors 38.

In order to retain switch member 30 in recess 14, I have provided a cover 50 for said chamber, such cover having a conventional toggle switch means 52 mounted in the central portion thereof arranged to actuate switch member 30 to move said switch member back and forth within chamber 14, a depression 54 being provided at the upper surface of said member substantially between the ends thereof adapted to be engaged by toggle switch means 52. Thus switch member 30 may be moved back and forth within recess 14, such recess being of a length suicient to permit connection of central connector 21 to either one or the other of outer connectors 17 or 25.

Since I have found it preferable to prevent sliding of the contacting surface of a switch conductor 38 along the bottom of recess 14 I have provided means for lifting said conductors vertically away from central connectors 17, 21 and 25, such means including buttons 60 mounted on the lower portion of connectors 38 and extending through insulating blocks 33. Depressions 61 are provided in the bottom surface of chamber 14 midway between conductor 21 or inner connector 20 and each of conductors 17 and 25 of outer connectors 16 and 24, so that when a connector 38 is in position to conduct current between conductor 21 and either of conductors 17 or 25, said button 60 will drop into its depression 61 and allow the ends of switch conductors 38 to contact the ends of said line conductors. Thus the depression 61 and its cooperating button60 operates to lift the ends of a U-shaped conductor 32 'away from the ends ofits coaxial line central conductors when the switch member 30 is moved from operative position.

It should be observed that the insulating'blocks 33 are so shaped as to leave open air spaces at the ends of cavities 32 at the region adjacent to the knee of the U shaped conductors 38. It is here provided for the purpose of speeding up the electromagnetic wave around the longer path which it follows inmaking the turn around the bends of the conductors 38 so that the phase relationship of the electric held at the inner corner and the outside corner is not materially disturbed. That is, the velocity of the electromagnetic wave in the dielectric media of the open air spaces land the insulating blocks remains in approximately the same ratio, so that the phase relationship of the electric field of the electromagnetic wave is maintained substantially unchanged.

The web 34 between waveguide cavities is effective to prevent feedback from the operative lines to the unused line by terminating the inoperative line by confining the end of said line within a completely ,enclosed metallic boundary. This arrangement provides extremely high attenuation to the signal being fed back into the unused line through the switch since then the only means by which leakage can occur is through the spaces between the sliding surfaces of body 12 and switch member 30, and such spaces can be made exceedingly narrow.

As above indicated, an important advantage of this switch construction is the fact that it provides a fixed unbroken boundary path for the current carriedrby the outer boundary of a waveguide which path is outside the movable switch member body. No current need flow through the switch slide member.

If the boundary was not so maintained the resulting standing wave ratio would be discontinuous with sharp peaks appearing irregularly and unpredictably across the radio frequency band, this etect being produced by poor contact between the sliding switch member and the switch body at the critical point of transmission of the electromagnetic wave, that is, at the meeting faces of the movable swich member and the switch body. Furthermore, in this switch, the electromagnetic field pattern is confined to one switch channel only and that channel is isolated from all other channels.

As will be obvious to those skilled in this art, the number and arrangement of the connectors with which the switch body is equipped necessarily will be varied to suit the .requirements of individual situations. This construction, as pointed out above is as 'applicable to true waveguides as to co-axial lines and, consequently, the term waveguide switch as herein used should be understood to include true waveguides.

invention is susceptible of embodiment in other forms without departing from the spirit or scope thereof.

Having thus described my invention, what I desire to claim as new is:

1. A co-'axial switch including a switch body having a metallic walled recess therein, a plurality of co-axial line connections including central conductors in said switch body extending to said recess, a sliding switch member having an open sided metallic walled co-axial cavity While I have herein shown and described a preferredy embodiment of my invention, it will be evident that the therein including a central conductor arranged to connect two of said co-axial'line connections in one switch position, Said member being mounted for sliding linear movement in said recess and together with the metallic recess wall providing in said one switch position a c0- axial line of uniform impedance with the metallic recess wall forming a continuous unbroken longitudinal portion of the boundary of said line, whereby said switch provides in said one position a co-axial line of uniform im pedance throughout its length with a continuous conducting path along the boundary of said line. i 2. A co-axial switch including a switch body having i' )a metallic walled recess therein, a plurality of co-axial line connections including central conductors in said switch body extending to said recess, a sliding switch member having an open sided metallic walled co-axial cavity therein including a U-shaped central conductor arranged to connect two of said co-axial line connections in one switch position, said member being mounted for sliding linear movement in said recess and together with the` metallic recess wall providing in said one Iswitch position a co-axial line of uniform impedance with the metallic recess wall forming a continuous unbroken longitudinal portion of the boundary. of said line whereby said switch provides in said one position a co-axial line of uniform impedance throughout its lengthV with -a continuous conducting path along the boundary of said line.

3. A co-aXial switch as claimed in claim 2 in which the U shaped central conductor in said co-aXial cavity is mounted for limited sideway movement transversely of said cavity, spring means being provided to urge the ends of said U-shaped central conductor into firm pressure contact with the ends of the central conductors of said co-axial line connections in said one position.

4. A co-axial'switch as claimed in claim 3 further having lifting means operable to move the ends of said U shaped central conductor away from the ends of said co-axial line central conductors when said switch member is moved Vfrom said one position.

5. A co-axial switch 'as claimed in claim 4 in which said lifting. means includes a depression in said metallic recess bottom wall and button means on said U shaped central conductor cooperating vertically to move the ends of said U shaped central conductor.

References Cited in the le of this patent UNITED STATES PATENTS 319,649 Wetherill JuneS, 1885 2,344,780 Kram Mar. 21, 1944 .2,432,476 Hesse Dec..9, 1947i 2,475,647 Spriggs July 12, 1949i 2,508,479 Wheeler May 23, 1950 2,550,921 Greene May 1, 1951 FOREIGN PATENTS 903,612 France Jan. 22, 1945 

